Fractional Distillation and Crude Oil

Fractional distillation is a process that separates the components in a mixture based on their different boiling points.

Crude oil is a complex mixture of hydrocarbons extracted from the ground. In its raw form, crude oil is not very useful because its properties and composition vary widely. To make crude oil useful, it must be broken down into simpler mixtures. These mixtures, called fractions, contain hydrocarbons with similar carbon chain lengths and properties.

We can separate the various hydrocarbons in crude oil as they all have different boiling points. By breaking down crude oil into these different fractions, we can isolate the specific hydrocarbons we need for various purposes. This allows us to make use of the different properties of each fraction to create a wide range of useful products.

Process of Fractional Distillation with Crude oil

Let’s look at how the process of fractional distillation works with crude oil:

1. Heated crude oil enters the fractionating column at the bottom, and the vapours rise up through the column.

  • The column is hotter at the bottom and becomes cooler towards the top

2. As the vapours rise, hydrocarbons with higher boiling points start to condense into liquids at lower temperatures, towards the bottom of the column.

3. Hydrocarbons with lower boiling points continue to rise further up the column.

4. As the different hydrocarbons reach different heights in the column, they condense into liquids at different temperatures, forming separate fractions. Once the hydrocarbons condense into a liquid, they are drawn off from the column.

Diagram illustrating the distillation of crude oil in a furnace and the various products derived at different temperatures. Starting from the top, products include: Liquid petroleum gas (with an icon of a gas cylinder), Petrol or Gasoline (with a car icon), Naphtha (with a flame icon), Paraffin (with an aeroplane icon), Diesel (with a lorry icon), Fuel Oil (with a ship icon), Lubricating Oil (with an oil can icon), and Bitumen (with a road icon).

The separation of the hydrocarbons in crude oil occurs because different hydrocarbons have different boiling points.

Long-chain hydrocarbons have stronger intermolecular forces and therefore higher boiling points. These hydrocarbons require more energy to break the forces of attraction between their molecules. As a result, they evaporate and condense in the fractions near the bottom of the fractionating column.

Short-chain hydrocarbons have weaker intermolecular forces and therefore lower boiling points. This means that they will stay as a gas for much longer and rise further up the column. Less energy is required to break the forces of attraction between their molecules. As a result, they condense in the fractions near the top of the column.

Petrochemicals

Petrochemicals are substances that we get from crude oil. These substances are used as feedstocks, which means raw materials. The petrochemical industry then transforms these feedstocks into a wide range of products with various uses, including:

  • Solvents
  • Lubricants
  • Detergents
  • Polymers

Crude oil is also useful as fuel. Different fractions of crude oil have different properties and can be used for various purposes. Here’s a table showing the different fractions of crude oil and their uses:

FractionUse
Liquified petroleum gasesDomestic cooking and heating
PetrolFuel for cars
KeroseneFuel for aircrafts
Diesel oilFuel for some vehicles
Heavy fuel oilFuel for ships and power stations
BitumenSurface roads and roofs

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